1. Technical Field
The present invention relates to a plasma display panel (PDP) for displaying an image by use of gas discharge.
2. Related Art
In general, a PDP is a display device in which plasma generated by gas discharge emits vacuum ultra-violet (VUV) light, the VUV light excites phosphor layers, and an image is displayed using visible light of red (R), green (G), and blue (B). The PDP with a large-sized display screen of 60 inches or more can be realized in a thickness of 10 cm or less. Since the PDP is a self-emitting display device like a cathode ray tube (CRT), it provides outstanding color reproducibility and wide viewing angle. Further, since the PDP is more advantageous than a liquid crystal display (LCD) in terms of fabrication process, productivity, and cost, it is becoming popular as a flat panel display for televisions and computers.
An alternating current (AC) PDP includes rear and front substrates. The rear substrate has address electrodes formed thereon. A dielectric layer is formed on the inner surface of the rear substrate and covers the address electrodes. Stripe-shaped barrier ribs are provided between the address electrodes on the dielectric layer. Phosphor layers of R, G, and B primary colors are provided between the barrier ribs. The front substrate which opposes the rear substrate has, on one surface, display electrodes consisting of a pair of transparent and bus electrodes formed in a direction intersecting with the address electrodes. A dielectric layer and an MgO protective film are sequentially formed on the inner surface of front substrate while covering the display electrodes. Discharge cells are formed at locations where the address electrodes on the rear substrate and the display electrodes on the front substrate intersect each other. Millions of unit discharge cells are arranged in a matrix form within the PDP. The discharge cells in AC PDP arranged in a matrix form are driven using memory characteristics.
In more detail, to generate discharge between a pair of display electrodes consisting of X- and Y-electrodes, a potential difference of a predetermined voltage or more is required, which is called a firing voltage Vf. When a scan pulse and an addressing voltage Va are applied to the Y-electrode and the address electrode, respectively, discharge is initiated between the two electrodes, whereby plasma is formed in a selected discharge cell. Electrons and ions within the plasma move to an electrode having an opposite polarity to thereby generate a current.
Each electrode of the AC PDP is covered with a dielectric layer, such that most of the space charges are accumulated on the dielectric layer having opposite polarity. Accordingly, a net space potential between the Y-electrode and the address electrode becomes smaller than the originally applied addressing voltage Va, so that discharge weakens and address discharge disappears. A relatively small amount of electrons are accumulated on the X-electrode, while a relatively large amount of ions are accumulated on the Y-electrode. The electrical charges accumulated on the dielectric layer covering the X- and Y-electrodes are referred to as wall charges Qw. The space voltage formed between the X- and Y-electrodes by the wall charges is referred to as wall voltage Vw.
When a constant sustain discharge voltage Vs is applied between the X- and Y-electrodes, for example, when a sum Vs+Vw of the sustain discharge voltage Vs and the wall voltage Vw is greater than the discharge firing voltage Vf, discharge occurs within the discharge cell. VUV light generated at this time excites phosphor layers to emit visible light through the transparent front substrate.
However, when address discharge is not generated between the Y-electrode and the address electrode (i.e. when the addressing voltage Va is not applied), wall charges are not accumulated between the X- and Y-electrodes. As such, a wall voltage is not present between the X- and Y-electrodes. In this case, only the sustain discharge voltage Vs applied between the X- and Y-electrodes is formed in the discharge cell. Since this voltage Vs is lower than the discharge firing voltage Vf, discharge does not occur in the space between the X- and Y-electrodes.
The PDP, which is driven as above, has a pair of X- and Y-electrodes within each discharge cell. Accordingly, after a reset period, address discharge occurs during an address period at a location of the discharge cell where the Y-electrode and the address electrode intersect each other. During the subsequent sustain period, sustain discharge occurs at a location of the discharge cell between the X- and Y-electrodes.
In the PDP, surface discharge occurs between the X- and Y-electrodes at the center of the discharge cell. As a result, as the distance from the center of the discharge cell increases, the density and density uniformity of plasma generating surface discharge becomes remarkably weak, thereby decreasing discharge efficiency and brightness.